1. Technical Field
The present invention is concerned with an optical communications system, in particular a protected optical communication system having a main supply arm and a back up supply arm.
2. Related Art
In a so-called Passive Optical Network or PON, a plurality of terminals are connected to a supply arm by a distribution network having a plurality of splitter junctions arranged in a tree structure. The supply arm is normally formed by a head end arranged along an optical path, and, in the case of a long reach PON, may include a repeater. For fault tolerance purposes, it is known to provide a back up supply arm, also connected to the distribution network. The back up supply arm duplicates the function of the main supply arm, so that if a fault occurs in the main supply arm, the back up supply arm can take over. However, the back up supply arm is normally required to perform an initialisation routine when it takes over. This initialisation routine can involve a ranging procedure which can be excessively time consuming.